This invention relates to a roll cleaning device, particularly for the fixing roll of a pressure fixing roll pair which serves for the fixing of a toner image formed of a toner powder made of a synthetic (plastic) material. The device finds particular application in an electrostatic copier and includes a cleaning felt impregnated with silicone oil.
Conventionally, in the direct or indirect electrostatic copying process, for the fixing of a developed image formed of a proper toner on a permanent record carrier, various fixing processes may be used. According to a known fixing process, the permanent record carrier (such as a paper sheet) is passed between a heated fixing roll and a pressure roll which is in engagement with the fixing roll. During this step the powder of the toner image is melted on the sheet and is caused to adhere thereto. This process, however, still has certain drawbacks. A portion of the toner sticks to the circumferential surface of the fixing roll which contacts the toner image; these adhered residues then are transferred to the consecutive record carrier, thus causing soiling thereof. In case the temperature of the fixing roll is too low, unmelted powder adheres thereto and is pressed, in an offset-like manner, onto the successive record carriers. If, on the contrary, the temperature of the fixing roll is too high, melted powder may adhere thereto and again, soil the successive sheets. In order to prevent such an offset soiling of the permanent record carriers, it is necessary to carefully control the fixing temperature. Such a control of the fixing temperature is, however, wrought with difficulties.
More recently, due to the availability of new toners, another fixing process has been introduced wherein the toner image is fixed without the use of heat by means of generating a sufficiently high pressure between the two rolls. In this process too, after the pressure fixing, a certain quantity of toner remains on the circumferential surface of the fixing roll which had contacted the toner image; these toner portions have to be removed as well, since the residual toner adhering to the fixing roll would again lead to the above-noted offset soiling of the record carriers.
It is known to arrange a silicone oil-impregnated cleaning felt in contact with the fixing roll to prevent the above-outlined offset soiling. The cleaning felt is conventionally formed of a thick felt strip which is inserted in a U-shaped holder and is immobilized on both sides. This arrangement is disadvantageous, in that the cleaning felt, as a whole, has a very limited continuous service life; thus, it has to be replaced very frequently. In the known device, however, the felt has to be replaced together with its holder to which it is firmly affixed. This circumstance adds substantially to the cost of the refill felts. Further, such a replacement needs particular skill; it thus cannot be performed by the user of the copier; it has to be effected by servicing personnel.